1. Field of the Invention
This invention relates to audio storage and distribution systems, and in particular to digital communication systems which may be remotely controlled from a plurality of user locations.
2. Description of the Prior Art
The present state-of-the-art audio distribution systems may be classified into two general groups. The first type of audio system utilizes a central source of audio programming which transmits a sequence of audio program material over a master communications distribution system to a plurality of user locations. The user has no control over the sequence of the audio programming other than to adjust the volume, to change channels or to turn the programming on and off. The MUZAK music subcarrier system authorized by the Federal Communications Commission is one common example of this type of audio system.
A second type of audio system employs a master control center having a plurality of available audio program material which may be selected and sequentially arranged from a user center located nearby. In this second type of system the user may select and sequentially arrange several of the available programs. However, the communications requirements of this second type of system generally limits the separation between each of the user stations and the master control station to a relatively small geographic area. A common example of this type of system is the remote controlled audio system utilized by libraries or large universities to distribute audio program material to various remotely located student centers.
In contrast, the present invention uses a master data bank located at a central location which is coupled to a plurality of user locations by common communication lines, such as narrow band or wide band telephone lines. Special signal processing is accomplished both before the signal is transmitted over the lines and after the signal is received at the user location to optimize the signal quality to suit the particular limitations of the communications system. Each remotely located user position also includes a command section for generating a command signal over the communications line for being received at the central data location for selecting the desired sequence of the stored programs.
The prior art contains several examples of the type of technology required to implement this system. Von Muench in U.S. Pat. No. 3,626,096 discloses the use of a microphone coupled to an analog to digital converter for digitizing the analog signal. Palus in U.S. Pat. No. 3,444,550 discloses a system utilizing a logarithmic amplifier driving an analog to digital converter. Digital data transmission systems (MODEMS) of the type disclosed by Forney et al. in U.S. Pat. No. 3,887,768 and Ragsdale et al. in U.S. Pat. No. 3,643,023 are well known in the art.